<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>

        * {
            margin: 0;
            padding: 0;
        }

        .outer {
            height: 100px;
            display: flex;
            flex-direction: row;
            justify-content: space-between;
        }

        .left {
            width: 200px;
            height: 100%;
            background: lightcoral;
            text-align: center;
            line-height: 100px;
            flex: 1;
        }

        .middle {
            width: 200px;
            height: 100%;
            background: antiquewhite;
            text-align: center;
            line-height: 100px;
            flex: 2;
        }

        .right {
            width: 200px;
            height: 100%;
            background: lightseagreen;
            text-align: center;
            line-height: 100px;
            flex: 1;
        }
    </style>
</head>

<body>
</body>
<div class="outer">
    <div class="left">left</div>
    <div class="middle">middle</div>
    <div class="right">right</div>
</div>


</body>

</html>